Vitamin D deficiency and depression in diabetes mellitus: A systematic review and meta-analysis

Diabetes mellitus (DM) is a major global health concern with rising prevalence and significant comorbidities. Among modifiable risk factors, vitamin D (VD) deficiency has been increasingly associated with both the development of DM and the presence of depressive symptoms. Given the relevance of psychological health in diabetes management, exploring the interrelationship between VD, depression, and diabetes is of growing scientific interest. To investigate this triad, we conducted a systematic review of human cohort studies across PubMed and Web of Science, focusing on the relationship between VD status and depression in diabetic patients. Meta-analyses were performed with Review Manager (RevMan 5.3, Cochrane, London, United Kingdom) using the inverse variance method, and funnel plots assessed publication bias. Despite the limited and heterogeneous literature, pooled analyses revealed a significant inverse association between VD levels and depression in diabetes (OR, 0.90, 95%CI, 0.84-0.96). Future longitudinal and interventional studies are needed to clarify causal pathways, considering sex differences and body composition. Confirming this relationship could inform preventive strategies that improve the quality of life of diabetic patients through targeted nutritional and vitamin-based interventions.